Cross-continental patterns in the timing of southward Peregrine Falcon migration in North America

We analyzed the timing of southward migration of Peregrine Falcons (Falco peregrinus) across North America, based on passage data compiled by the Hawk Migration Association of North America, supplemented with two other similar datasets collected by individual observers at sites in western Canada. The results show two distinct continental-scale patterns. First, the north to south progression of peak peregrine passage down the continent is readily apparent, occurring primarily during September and October. Second, the movement of Peregrine Falcons is earlier by 4¿6 wk on the west coast than on the eastern seaboard, and is intermediate at inland sites. The wavefront of Peregrine Falcons advancing southward is oriented from southwest to northeast across the North American continent. We hypothesize that these patterns have implications for the southward migrations of potential prey species, which may select routes or times to avoid places of high risk due to Peregrine Falcons.